1. Field of the Invention
The present invention concerns cleaning plugging deposits from packed fiber bed type mist eliminators particularly mist eliminators used to process combustion flue gases.
2. Description of the Prior Art
Packed fiber bed mist eliminators are devices designed for processing gases containing liquid mists and/or particulate matter. The gases impinge upon the fibers and the liquid and/or particulate matter are deposited upon the fibers. As liquid droplets build up on the fibers, they tend to run off (usually down) into a collection area or reservoir for removal. Some solid particles may run off with the liquid while liquid soluble particles tend to dissolve in the liquid. Usually the liquid contains water. Typically, sulfur dioxide is removed from gases such as combustion gases by an absorber or scrubber which can result in an ammonium sulfate mist in the gas.
Some particulate matter may become firmly attached to the fibers or become embedded onto the fiber bed. Such particulate deposits tend to plug the mist eliminators. Such deposits can be carbonaceous and/or inorganic and are mostly water insoluble.
Prior to the present invention, one method of cleaning the plugging materials from packed fiber bed mist eliminators was by removing individual mist eliminator elements from their containing vessels and manually washing them with water sprays. Alternatively, back-flow systems or repeated filling of the vessels with water, followed by rapid draining has been tried to mechanically loosen and flush away the plugging contaminants. Large mist eliminators have been cleaned by maintenance personnel entering the vessel with high pressure water spray nozzles to individually wash mist eliminator elements in place by mechanically dislodging the plugging materials with a high pressure water spray.
In addition to the physical cleaning processes designed to dislodge plugging materials by the application of force there have been some attempts at chemical cleaning procedures. However, because of the materials of construction of the vessels and the fiber demisting elements, strong chemical treatments had to be avoided because of possible damage to the vessel or fiber elements. Accordingly, dilute chemical treatment such as dilute hydrochloric acid or dilute acidified sodium hypochlorite solutions have been tried with limited success.
The disadvantages of such prior art treatment procedures for cleaning fiber bed mist eliminators are excessive labor requirements; possible damage to the mist eliminator elements caused by the forces involved in physically dislodging the plugging materials; incomplete cleaning with backwash or similar flushing procedures; and excessive space required between fiber bed elements to provide access areas for maintenance personnel during cleaning.
An object of the present invention is to allow cleaning of the mist eliminator elements in situ regardless of vessel or element spacing or configuration without seriously attacking and degrading the fiber bed elements or vessel materials by employing a chemical soaking technique which also minimizes the labor requirements.